Advantageously used as a developing roller, a charging roller or the like to be incorporated in an electrophotographic image forming apparatus is a semiconductive roller which includes a roller body produced by forming a semiconductive rubber composition into a tubular body and crosslinking the tubular body in order to provide sufficient abutment nip with respect to a photoreceptor body or the like and properly impart the roller with the corresponding function.
In order to control the roller resistance of the semiconductive roller within a roller resistance range that is suitable for the developing roller, the charging roller or the like, an ion conductive rubber such as epichlorohydrin rubber is often used as a rubber component for the rubber composition.
Further, diene rubber is often used in combination with the ion conductive rubber as the rubber component in order to impart the rubber composition with proper processability, to improve the mechanical strength, the durability and the like of the roller body, or to impart the roller body with proper rubber characteristic properties, i.e., to make the roller body flexible and less susceptible to permanent compressive deformation with a reduced compression set.
The rubber composition further contains a crosslinking component for crosslinking the rubber component.
In Patent Document 1 (JP2014-80456A), for example, sulfur crosslinking agent, a thiourea compound, a thiuram accelerating agent and a thiazole accelerating agent are used in combination as the crosslinking component. Sulfur is used as the sulfur crosslinking agent.
Patent Document 1 states that these compounds are used in predetermined proportions as the crosslinking component, whereby the roller body is imparted with lower hardness and hence higher flexibility and a reduced compression set to be thereby further advantageously prevented from suffering from uneven image formation which may otherwise occur due to the permanent compressive deformation.